The present invention relates to an underground drain pipe, such as a culvert drain pipe, which is used to collect underground water and conduct it to a disposal channel.
Several underground drain pipes of the same type to which the present invention pertains have been proposed. In one case, the pipe is formed with a number of small holes formed through the wall of the pipe. Another example of a conventional pipe was proposed by the present applicant is illustrated in FIG. 1. This pipe is constructed by spirally winding a band 02 of unwoven cloth having therein a large number of small holes 011 with a predetermined spacing between adjacent edges of the band 02. A separately formed thick band 01 of a hard synthetic resin is would over the gap formed between adjacent edges of the band 02 of unwoven cloth. Adjacent edge portions 022 and 023 of the band 02 of unwoven cloth are joined to respective edge portions 011 and 012 of the thick band 01 of hard synthetic resin.
A drain pipe having holes formed in the pipe wall after production of the pipe itself is disadvantageous in that the holing work is troublesome. Moreover, the pipe of FIG. 1 is disadvantageous in that, although it does not require holing work, problems are involved in cutting and joining the unwoven cloth. Particularly, if the diameter of the pipe is large, for instance, 500 mm or 1000 mm, the soil pressure is often sufficient to break the unwoven cloth. Also, there is a tendancy for the seam joints between the unwoven cloth and the hard resin band to separate.